1. Field of the Invention
The present invention relates to an optical information recording medium, and more particularly to a phase-change optical information recording medium in which information is recorded, reproduced and rewritten by changing an optical property of a material in the recording layer thereof by irradiating the recording layer with a laser light beam. In addition, the present invention also relates to an information recording method and apparatus using the optical information recording medium.
2. Discussion of the Related Art
Various optical information recording media capable of recording and reproducing information upon irradiation of laser light thereto have been developed and used. Specific examples of such optical information recording media include CD-Rs and DVD-Rs, in which information can be written once, and CD-RWs, DVD-RWs, DVD-RAMs, MDs and MO disks, in which information can be rewritten. These optical information media are removable and therefore the demand therefor has been increasing year by year.
Among these optical information recording media, CD-RWs, DVD-RWs, DVD-RAMs, etc. use phase-change materials in their recording layers, i.e., utilize changes between a crystal phase and non-crystal phase or between crystal phases. Particularly, magneto-optical memories such as MDs and MO disks have advantages such that overwriting can be performed using a single light beam, and in addition the optical systems of the record/reproduction devices which record and reproduce information in the magneto-optical memories are simple. Therefore the demand for these optical information recording media has been increasing.
In general, when information is recorded in a phase-change information recording medium, a pulse strategy in which the power level of the laser light used for recording and rewriting is changed so as to be three levels is used. When multi-speed recording and CAV (constant angular velocity) recording in which information is recorded in a recording medium at different linear speeds are performed using this pulse strategy, the energy needed for heating the recording layer of the recording medium to a predetermined temperature in high linear speed recording is greater than that in low linear speed recording, and therefore recording conditions in high linear speed recording have to be different from those in low linear speed recording. Accordingly, needs exist for techniques in which the recording power is increased in high linear speed recording, and/or the running time for a high level pulse having a power level Pw in a mp portion is lengthened in the high linear speed recording, to properly record information in a recording medium even when recording speed is changed, i.e., to record information having good recording properties in a recording medium.
In this case, the suitable recording conditions change depending on the materials used for the recording medium and construction of the recording medium. Therefore a technique is used for CD-RWs in which suitable recording conditions at each of the linear recording speeds, 1× (i.e., 1.2 m/s), 4× (4.8 m/s) and 10× (12 m/s) are input therein such that the recording devices can properly set the recording conditions using this information.
However, when such a technique is used, at first the suitable recording power and/or suitable record pulse strategy are determined for each linear recording speed and then suitable recording conditions have to be set for each linear recoding speed. Therefore, in CAV recording in which linear recording speed is continuously changed as the recording point moves in a diameter direction of a recording medium, the setting of suitable recording conditions is very difficult. Therefore, a need exits for a recording method in which information in good condition can be recorded even in such a case. Alternatively, a need exists for an optical information recording medium in which information in good condition can be recorded independently of the linear recording speed.